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Biomedical subjects

R Leder

Publications and source records attributed to R Leder.

13 recordsLinked to original sources
PubMed2000

Self-exciting chaos as a dynamic model for irregular neural spiking

We introduce a nonlinear dynamical system with self-exciting chaotic dynamics. Its interspike interval return map shows a noisy Poisson-like distribution. Spike sequences from different initial conditions are unrelated but possess the same mean frequency. In the presence of noisy perturbations, sequences started from different initial conditions synchronize. The features of the model are compared with experimental results for irregular spike sequences in neurons. Self-exciting chaos offers a mechanism for temporal coding of complex input signals.

Journal Article↗
PubMed1994

Efficacy and safety of iopromide for excretory urography.

RATIONALE AND OBJECTIVES: Iopromide is a nonionic monomeric contrast agent. Initial laboratory and clinical data have shown that it is relatively safe. Efficacy for excretory urography has been shown to be good, comparable with other low-osmolality agents. The authors attempted to confirm these impressions in a randomized, double-blind comparison with equivalent doses of ioversol and iopamidol. METHODS: Two hundred adult patients undergoing excretory urography were studied. One hundred received iopromide, 40 received ioversol, and 60 received iopamidol (300 mg I/kg) as an intravenous bolus. Urographic films (obtained 1, 5, 15, and 20 minutes after the bolus, and postvoid) were interpreted by an observer blinded to contrast type. Visualization of renal parenchyma, pelvis and calyces, ureters, and bladder was independently assessed as excellent, good, poor, or nonvisualized. Vital signs were recorded before, 30 to 60 minutes after, and 24 hours after injection. Adverse reactions were sought, physical examinations were performed, and standard hematology and serum chemistry values were measured before and 1 day after injection; a 72-hour serum creatinine level was also measured. RESULTS: Ninety-eight percent of visualization scores were good or excellent; no significant differences among iopromide, iopamidol, and ioversol were found, nor were there any significant differences among groups in vital signs. Only one patient experienced a contrast-related physical examination change (subcutaneous extravasation). No significant changes with regard to hematology or serum chemistry values were observed; there was no contrast-induced nephropathy. Mild adverse reactions were experienced by 10% of patients; there were no significant differences in reaction rates among contrast agents. CONCLUSIONS: Iopromide at a dose of approximately 300 mg I/kg is safe and effective as an excretory urographic agent and is comparable in performance with ioversol and iopamidol.

Adult↗
PubMed1994

Cost-effective use of low-osmolality contrast media for CT of the liver: evaluation of liver enhancement provided by various doses of iohexol.

OBJECTIVE: Because of pending efforts to reform health care in the United States, judicious use of low-osmolality contrast media is important. We studied the effects of using various concentrations and volumes of iohexol, compared with the conventional dose and concentration of diatrizoate meglumine used for CT, to determine if a more cost-effective dose results in diagnostically efficacious liver enhancement. SUBJECTS AND METHODS: A total of 902 patients received one of nine different doses of IV contrast media. Eight doses of iohexol were used: 125 ml of iohexol 350 (350 mg l/ml, 44 g l/dose), 100 ml of iohexol 350 (35 g l/dose), 150 ml of iohexol 300 (300 mg l/ml, 45 g l/dose), 120 ml of iohexol 300 (36 g l/dose), 100 ml of iohexol 300 (30 g l/dose), 175 ml of iohexol 240 (240 mg l/ml, 42 g l/dose), 150 ml of iohexol 240 (36 g l/dose), and 125 ml of iohexol 240 (30 g l/dose). A single dose (150 ml) of diatrizoate meglumine 60% (w/v) was used (42 g l/dose). Contrast material was injected at a rate of 2 ml/sec. Scanning began 35-45 sec after injection. Quantitative analysis of enhancement was performed by obtaining region-of-interest measurements through the liver on scans obtained before and after injection of contrast material. Mean and maximum changes in hepatic density and mean time to maximum enhancement were measured. Mean time-density curves were subsequently derived for each dose of contrast material. Qualitative analysis of enhancement was performed by using subjective, previously defined criteria. All studies were interpreted in a double-blind fashion. RESULTS: Mean hepatic enhancement was greater with 125 ml of iohexol 350 and 150 ml of iohexol 300 than with other doses of contrast material (p < .05). Both 125 ml of iohexol 350 and 150 ml of iohexol 300 produced actual hepatic enhancement of more than 50 H for over 60 sec. The greatest maximum increase in hepatic density occurred with 125 ml of iohexol 350. When analyzed qualitatively, 150 ml of iohexol 300 resulted in the highest percentage of optimum enhancement. CONCLUSION: According to quantitative analysis, 125 ml of iohexol 350 administered at a rate of 2 ml/sec produces the best enhancement, whereas according to qualitative analysis, 150 ml of iohexol 300 produces the best enhancement. All doses of iohexol 240 provide poor enhancement compared with a conventional dose of contrast material of 150 ml of diatrizoate meglumine 60% or 150 ml of iohexol 300. A moderate cost savings can be achieved by using 125 ml of iohexol 350 for dynamic sequential CT.

Cost-Benefit Analysis↗
PubMed1993

Contrast material for combined abdominal and pelvic CT: can cost be reduced by increasing the concentration and decreasing the volume?

OBJECTIVE: The purpose of this study was to determine if enhancement provided by a smaller volume of a more concentrated nonionic contrast agent is equivalent to that provided by a larger volume of a less concentrated nonionic agent on dynamic, incremental abdominal and pelvic CT. SUBJECTS AND METHODS: During a 4-month period, 168 patients undergoing dynamic incremental abdominal and pelvic CT received 150 ml iopamidol-300 (45 g iodine). During the following 4 months, 119 patients received 125 ml ioversol-320 (40 g iodine). The same automated injector and scanning parameters were used for both groups. Absolute enhancement of the liver at three levels and of abdominal and pelvic vessels was calculated and analyzed by using Student's t-test. RESULTS: Arterial and venous enhancement in the upper part of the abdomen, at the level of the iliac crest, or in the pelvis was not significantly different with the two contrast agents. Both ioversol and iopamidol provided the same mean enhancement of the hepatic parenchyma at the level of the hepatic veins (45 H) and at the level of the portal vein (49 H). At the level of the gallbladder fossa, enhancement of liver parenchyma with the two contrast agents was significantly different (p = .04): mean enhancement was 45 H for iopamidol and 42 H for ioversol. A retrospective analysis of the liver enhancement profiles from 50 randomly selected patients from each group showed no significant difference in parenchymal enhancement. CONCLUSION: For dynamic abdominal and pelvic CT, no statistically significant difference was found between the mean enhancement of the liver and abdominal vessels after administration of 125 ml of ioversol-320 and that after administration of 150 ml of iopamidol-300. Therefore, 125 ml of ioversol-320 can be used instead of 150 ml of iopamidol-300 without compromising image quality. At current prices, this will result in savings of approximately 18% per patient.

Abdomen↗
PubMed1992

Adrenal gland enlargement in major depression. A computed tomographic study.

To determine whether the well-documented hyperactivity of the hypothalamic-pituitary-adrenal axis in depressed patients includes adrenal gland hypertrophy, adrenal gland size was evaluated by computed tomography. Assessments consisted of (1) global ratings by two radiologists ignorant of the diagnostic identity of the subjects and (2) calculation of adrenal volume. Of the 38 patients with major depression, 12 were rated as exhibiting adrenal hypertrophy. Adrenal volumes in the depressed patients were significantly increased when compared with those of normal controls. Adrenal gland size was not correlated with dexamethasone suppression test results, patient age, duration of the depressive episode, or depression severity. These results are concordant with the hypothesis that chronic corticotropin hypersecretion in depression results in adrenocortical hypertrophy. Adrenal gland enlargement may be a measure of cumulative lifetime depression.

Adrenal Glands↗
PubMed1988

Response of delta (0-3 Hz) EEG and eye movement density to a night with 100 minutes of sleep.

In one of a series of experiments aimed at gathering the empirical data required to formulate mathematically our recovery model of sleep, we recently (1) measured the increase in delta electroencephalogram (EEG) following one night of total sleep deprivation (TSD). We found that the delta rebound was confined to the first non-rapid eye movement period (NREM-P1) of recovery sleep; this unexpected result was documented with direct computer measurement of 0-3 Hz EEG, as well as with visual scoring of stages 3 and 4. We also found a robust decrease in eye movement density during the second and third REM periods, which we hypothesized to be due to the increased depth of recovery sleep. In the present experiment, we awakened young adult subjects after 100 min of sleep, a duration that includes the first cycle for this age group, and analyzed visual and computer measures of delta and eye movement density during recovery sleep. We again found eye movement density to be significantly reduced in REM-P2 and P3, but to a lesser degree than after total sleep deprivation, a condition that may be presumed to produce a greater increase in sleep depth. Delta increases were again limited to the first cycle, although all subjects completed this cycle on the 100-min night. The major difference between recovery sleep patterns following the total deprivation and the 100-min sleep conditions was that 0-3-Hz wave amplitude increased significantly after the former, but not after the latter. In both studies, recovery sleep showed increased 0-3-Hz wave density. The neurophysiological implications of a response of EEG amplitude as opposed to wave density are briefly considered; separate measurement of these variables is more readily accomplished with period-amplitude than with spectral analysis. Our results further illustrate the importance of measuring sleep by physiological units, such as the successive NREMPs and REMPs. They also support other data that indicate that NREM-P1 plays a special role in human sleep: it responds selectively to sleep deprivation, shows the greatest ontogenetic variation across the human lifespan, and is the component of sleep that is most frequently abnormal in psychiatric patients. As we have long argued, it is inappropriate to conceptualize this high priority component of NREM sleep as "REM latency" and as a measure of REM "pressure" exclusively.

Adult↗
PubMed1983

Partial resolution of tardive dyskinesia with treatment of co-existing thyrotoxicosis.

Neuroleptic-induced tardive dyskinesia improved after treatment of thyrotoxicosis. Neuroleptic blood levels indicated that the improvement was not caused by masking of the symptoms by rising drug levels. Dopamine metabolite measurements suggested that the thyrotoxicosis caused an increase in the sensitivity of caudate neurons to dopamine, rather than a change in release of dopamine.

Dopamine↗
PubMed1980

Quantification of penile "buckling" force.

A hand-held transducer was developed for measuring penile rigidity. This instrument gives a quantitative measure of the force at which the penis "buckles." The transducer consists of a cantilever beam with strain gages that is rugged, easy to calibrate, and adaptable to most graphic recorders.

Humans↗